Field of the Invention
The disclosed information relates to an audio processing apparatus and an audio processing method.
Description of the Related Art
Noise reduction (NR) techniques are known as signal processing techniques for canceling or reducing noise contained in a signal of audio, a video image, and the like. One conventional audio NR technique is a method called spectral subtraction, which removes a removal target sound by subtracting a frequency component of audio that is the removal target by an amount corresponding to a gain of each thereof. The spectral subtraction is widely known as a basic technique of the NR techniques.
One NR technique developed by applying this technique is noise learning NR. The noise learning NR automatically learns a frequency region and a subtraction amount of a background sound or constantly occurring audio with use of an autocorrelation or an adaptive filter, and removes a frequency component thereof.
For example, a technique discussed in Japanese Patent Application Laid-Open No. 2009-49885 calculates a frequency characteristic contained in an input sound with use of an autocorrelation function, and determines whether the input sound is audio (voice) or surrounding noise. Then, the technique discussed in Japanese Patent Application Laid-Open No. 2009-49885 calculates an average value of the surrounding noise as an average noise, and subtracts the average noise from the input sound, thereby removing a surrounding noise component.
According to the technique discussed in Japanese Patent Application Laid-Open No. 2009-49885, a speed from the calculation of the frequency characteristic of the input sound to the removal of the surrounding noise component (i.e., a noise learning speed) is constant regardless of the surrounding noise. However, the surrounding noise may change depending on a time period of a day or the like. Therefore, the employment of the technique discussed in Japanese Patent Application Laid-Open No. 2009-49885 cannot achieve an accurate removal of the surrounding noise under such an environment that a level of the surrounding noise (a noise environment) changes depending on a time period of day.